From the viewpoints of energy problems and environmental problems, efficient reduction of CO2 using light energy, like plants, is demanded. Plants use a system referred to as the Z scheme, wherein light energy is excited in two steps. Based on the photochemical reaction of this system, plants oxidize water (H2O and OH−) to obtain electrons, and reduce carbon dioxide (CO2) to synthesize cellulose and saccharides.
However, the only techniques for artificially obtaining electrons from water to decompose CO2 via a photochemical reaction without using a sacrificial reagent are highly inefficient. Efficient reduction decomposition of CO2 requires efficient oxidation decomposition of water to obtain electrons.